1. Field of the Invention
The present invention relates to an engine block structure for a reciprocating engine, and, in more particularly, to a structure for a cylinder block of a multi-cylinder engine block that is provided with a water jacket on opposite sides of a raw of cylinders and oil return means for returning an oil for lubrication to oil source means from sliding parts and mechanisms.
2. Description of Related Art
There have been known various multi-cylinder reciprocating engines. Such an engine needs lubrication for the purposes of reducing wear and frictional losses of sliding parts of the engine, improving cooling efficiency of the sliding parts and dispersing impact pressure on the sliding parts. Specifically, an engine oil in an oil pan is sucked up by an oil pump and filtered by an oil filter, it is distributed to a main oil gallery in a cylinder block. The engine oil is distributed as a lubrication oil to sliding parts such as a crankshaft and pistons and mechanisms including sliding parts such as a valve drive mechanism installed to a cylinder head for cooling and lubrication of the sliding parts. The lubrication oil seeps out of the sliding parts and drops and then returns into the oil pan. The lubrication oil distributed to the crankshaft and the pistons escapes from sliding parts of the crankshaft and the pistons and seeps out of the sliding parts and drops directly to the oil pan. However, the lubrication oil distributed to, for example, the valve drive mechanism escapes from sliding parts such as camshafts and tappets and drops on a middle deck of the cylinder head. Then, the lubrication oil flows on the middle deck of the cylinder head and returns to the oil pan through oil return passages extending in both cylinder head and cylinder block.
In the case of a front engine-front drive system that is the mainstream of compact cars, it is general to install a power train from an engine to a differential as one whole transversely in an engine compartment. On the other hand, there are cars employing rear drive systems that provide drivers with satisfactory steering feelings. Such a rear drive car has an engine installed longitudinally in an engine compartment. In light of these circumstances, engines are preferable to be installed in both types of cars with only small or miner changes in structure.
However, in general, while a transverse engine that is installed transversely in the engine compartment places a crankshaft in a horizontal transverse direction, a longitudinal engine that is installed longitudinally in the engine compartment places a crankshaft a little inclined rearward down in most cases because it is accompanied by a transmission behind the engine. That is, there is a difference in inclination between the transverse engine and the longitudinal engine. Accordingly, an adverse influence is exerted on a flow of a lubrication oil in the oil return passages due to the positional difference. For example, in the case where an engine is installed transversely in the engine compartment, in order to cause a lubrication oil to drop from the cylinder head all around without staying in the cylinder head and to return to the oil pan, it can be thought to arrange a plurality of oil return passages at proper intervals along a straight row of cylinders. However, if this engine is installed longitudinally in the engine compartment, the lubrication oil is apt to stay near the rear end of the engine. Stagnation of a lubrication oil flow that occurs due to a stay of the lubrication oil is possibly one of causes of seizure of the sliding parts due to breaking of oil films.
In this regard, it can be thought to provide the cylinder head and/or the cylinder block with additional oil return passages at their rear end portions. However, it is very hard for the cylinder block to have oil return passages having desired sizes and shapes at the rear end portion. This is because, in light of providing an entire power train with a sufficient rigidity, the additional oil return passages exert a rigid restraint on a structure of the rear end portion of the cylinder block in which a coupling mount to which a transmission is coupled is.
Further, some engine block has a cylinder block provided with a water jacket that surrounds a straight row of cylinders of an in-line cylinder engine. In this cylinder block, as disclosed in, for example, Japanese Unexamined Patent Publication No. 10-141154, the water jacket comprises two parts of water jacket, an intake side water jacket and an exhaust side water jacket, disposed on opposite sides of the straight row of cylinders, respectively, that are connected to each other at front and rear ends thereof by front and rear communication channels, respectively. Cooling water is introduced into the water jacket through one of the communication channels. A water pump that supplies the cooling water is disposed on one of opposite side walls of the cylinder block near front end of the cylinder block and driven by a crankshaft of the engine through a V-belt.
Generally, in the engine block, cooling water is discharged from the water pump and enters the water jacket through front end of either one part of the water jacket. It is not always easy to appropriately divide a cooling water stream into two parts for the intake side water jacket and the exhaust side water jacket. In this regard, the prior art cylinder block has a water guide passage formed separately from the front communication channel of the water jacket in a front end wall of the cylinder block. According to the prior art cylinder block, cooling water is directed to a front position of the cylinder block through the water guide passage and then introduced into both intake side water jacket and exhaust water jacket. This separate water guide passage makes the cylinder block large in overall length. In addition, although on behalf of providing reliable distribution of cooling water into the intake side water jacket and the exhaust side water jacket, because the prior art cylinder block causes the cooling water stream to sharply turn after a stay at an end of the water guide passage, the distribution of cooling water to the water jacket is hard to be smooth and, in consequence, there possibly occurs an increase in mechanical loss in driving the water pump.
It is an object of the present invention to provide an engine block structure for a reciprocating engine in which a cylinder block at a rear end portion is provided with oil return passages showing reliable oil returning performance.
It is another object of the present invention to provide an engine block structure for a reciprocating engine including a cylinder block provided with a water jacket surrounding a row of cylinders that has a shortened overall length.
It is another object of the present invention to an engine block structure for a reciprocating engine including a cylinder block provided with a water jacket surrounding a row of cylinders that provides improved performance of introducing and distributing cooling water into a water jacket on opposite sides of the row of cylinders.
The above objects are achieved by an engine block structure including an cylinder block that is provided with a plurality of oil return passages formed along the straight row of cylinders in each of opposite side walls of a cylinder block. Each of the oil return passage extends approximately straight from top to bottom of the cylinder block between each adjacent cylinders so as to reliably return a lubrication oil which is the basic performance of the oil return passage. In addition to the oil return passages, the cylinder block is provided with an auxiliary oil return passage that extends from the rear top of the cylinder block to the middle of the oil return passage with an effect of preventing the lubrication oil from staying in the oil return passage.
According to a preferred embodiment of the invention, in the engine block structure including a cylinder block that is provided with a straight row of cylinders formed with a coupling mount located at a rear end wall of the cylinder block in a lengthwise direction to which a transmission is mounted, oil supply means for supplying an engine oil to sliding parts that are installed to the engine block from oil source means as lubrication oil, and oil return means for returning the lubrication oil to the oil source means from the sliding parts, the oil return means comprises a plurality of oil return passages formed along the straight row of cylinders in each of opposite side walls of the cylinder block, each of which extends straight from top to bottom of the cylinder block between each adjacent cylinders and a branch oil return passage which branches off from one of the oil return passages that is closest to the rear end wall of the cylinder block (a rearmost oil return passage) and extends obliquely upper toward the rear end wall of the cylinder block and opens in the top of the cylinder block. The end opening of the branch oil return passage is located closer to the rear end wall of the cylinder block than the end opening of the rearmost oil return passage opening in the top surface of the cylinder block.
The oil return passage that extends approximately straight from top to bottom of the cylinder block between each adjacent cylinders causes a lubrication oil that seeps out of the sliding parts to smoothly flow through the oil return passage and drop into an oil pan. This provides the engine block with reliable oil returning performance. In addition, while on one hand the arrangement of the oil return passages in which the oil return passage is kept away from positional interference with the cylinders securely provides the oil return passage with a sufficiently large cross sectional area, the arrangement of the oil return passages allows the cylinder block to be compact in configuration. Furthermore, the arrangement of the oil return passages causes the lubrication oil to drop into the oil pan in a position between the adjacent cylinders, so that counterweights of a crankshaft splash about only a small amount of the engine oil in the oil pan.
The branch oil return passage branching off from the rearmost oil return passages that is closest to the rear end wall of the cylinder block and extending obliquely upper toward the rear end wall of the cylinder block prevents the lubrication oil from staying at a rear portion of the cylinder head when the engine, even longitudinally installed in an engine compartment, is inclined with the rear end put lower in vertical position than the front end. Because, although the branch oil return passage has an upstream end opening in the top surface of the cylinder block in close proximity to the end wall of the cylinder block, it joins the oil return passage in a position relatively forward from the upstream end, there is no positional interference between the branch oil return passage and the coupling mount for the transmission.
The cylinder block may further comprise a pit for receiving a pinion of a starter motor therein which is formed so as to open ranging at least from one of the opposite side walls of the cylinder block below the branch oil return passage and to the rear end wall of the cylinder block. This pit is effectively used to enable easy installation of a transmission to the cylinder block. Although, in the case where an cylinder head is formed with the pit ranging from one side wall to the rear wall of the cylinder block, it is practically hard to form such a branch oil return passage as to extend vertically along the rear end of cylinder head because of positional interference with a coupling mount of the cylinder head to which a transmission is mounted, the engine block of the present invention having the branch oil return passage that has the upstream end opening in the top surface of the cylinder block in close proximity to the end wall of the cylinder block and joining the middle of the oil return passage is not exposed to any positional interference between the branch oil return passage and the coupling mount.
The cylinder block is further provided with a water jacket formed partly in one of the opposite sides of the straight row of cylinders and partly in another side of the straight row of cylinders. The branch oil return passage is laid so as to branch off from the oil return passage near below a bottom of the water jacket. According to this arrangement the branch oil return passage is such as to cross the water jacket obliquely as viewed in a vertical direction between the rearmost oil return passage and the rear end of the cylinder block. This structure provides the cylinder with an increased rigidity, which results in an increased coupling strength between the cylinder block and a transmission and a reduction in wall vibration and noise of the engine.
The cylinder block may further comprise a thermostat housing as an integral part of one of the opposite side walls of the cylinder head for receiving a thermostat therein. The thermostat housing is such as to project externally from the side wall in a position close to a front end wall of the cylinder block and corresponding to the water jacket. The cylinder block receives the greatest exciting force in a position corresponding to a combustion chamber of the cylinder, i.e. in a position of the side wall where the water jacket is formed. Accordingly, the cylinder block of the present invention that is formed integrally with the thermostat housing as an integral part of the side wall of the cylinder head is provided with an improved rigidity. This makes it possible to provide the cylinder block with a stiffening rib ranging from the thermostat housing to the rearmost return oil passage in order to increase an overall rigidity of the cylinder block with an effect of reducing wall vibrations.
The cylinder block may further comprise an external raise formed on each of the opposite side walls and an intermediate external raise formed as wall strengthening parts on each of the opposite side walls. The external raise is such as to be adjacent to each of foremost and rearmost oil return passages and the intermediate external raise is such as to continuously lead to both the external raises. The external raise adjacent to the foremost oil return passage is a continuous part of the thermostat housing, and the intermediate external raise is formed with a chamber for receiving an oil separator therein. The cylinder block at an upper portion of the side wall that receives exciting force most hardly is provided with a sufficiently enhanced rigidity by virtue of the integrated structure of the external raises and the thermostat housing as well as the location of the branch oil return passage This prevents or significantly reduces wall vibrations of the side wall of the cylinder block and, as a result, the engine and its associated devices generate only reduced wall vibration and noises. The intermediate external raise is formed with an oil separator chamber therein. The layout of these structural parts of the cylinder block including the thermostat housing, the oil return passages and oil separator chamber realizes a strengthened side wall of the cylinder block, which is contributory to providing the cylinder block having an increased rigidity, a decrease weight and compactness.
The cylinder block that has such a water jacket as extending partly on one side of the straight row of cylinders and partly on another side of the straight row of cylinders may further comprise a water guide passage through which cooling water is introduced into the water jacket at a position adjacent to an extreme or foremost one of the cylinders and director means disposed in the water guide passage near an interface between the water jacket and the water guide passage for directing the cooling water introduced into the water jacket with an effect of causing cooling water to flow smoothly into the water jacket.
Specifically, the director means comprises a generally triangular pillar which extends along an approximately full depth of the water jacket and is formed with a bolt hole in which a head bolt is fastened to install a cylinder head to the cylinder block therein. The triangular pillar is such that first one of three side walls of the triangular pillar that is adjacent to an external wall of the foremost cylinder is approximately perpendicular to a line passing vertical center axes of the foremost cylinder and the bolt hole, an edge line between second and third side walls of the triangular pillar being in the interface, the second side wall operating to direct a cooling water stream partly to the water jacket on one of opposite sides of the straight row of cylinders, and the third side wall directing the cooling water stream partly to the water jacket on another side of the opposite sides of the straight row of cylinders in cooperation with the front end wall of the cylinder block.
The triangular pillar divides a cooling water stream introduced to the water jacket through the water guide passage into two parts on opposite sides of the edge line of the triangular pillar. Then, the second side wall directs one cooling water stream into the water jacket on one side of the straight row of cylinders and the third side wall directs another cooling water stream to the water jacket on another side of the straight row of cylinders in cooperation with the front end wall of the cylinder block. As a result, while the cooling water stream is smoothly introduced into the water jacket, the cooling water stream is appropriately distributed on opposite sides of the straight row of cylinders. In addition, in the case for example where the engine block is provided with a water pump on one of opposite walls of the cylinder block as conventionally, according to the relative position between the edge line of the triangular pillar as director means and the water guide passage, the triangular pillar and the water guide passage overlap in position each other. This layout allows the cylinder block to be comparatively shorter as compared with a layout in which the triangular pillar and the water guide passage are not overlapped in position.
The triangular pillar has the first wall in approximately parallel to the external wall of the foremost cylinder. The cooling water flows between the triangular pillar and the external wall of the foremost cylinder without hindrance, which result in satisfactory cooling performance. The triangular pillar is such that the cross section has a comparatively long distance in a radial direction of the foremost cylinder, so as to have a sufficiently high bending rigidity.
The water guide passage may be formed in one of the opposite side walls of the cylinder block to which an intake manifold is installed so that the water jacket is provided with a width that is greater between the third wall of the triangular pillar and the front end wall of the cylinder block than between the second side wall of the triangular pillar and the intake side wall of the cylinder block. This configuration of the water jacket provides the water jacket with a larger amount of cooling water on the exhaust side at which the cylinder block is exposed to a comparatively high temperature than on the exhaust side. As a result, the cylinder block is entirely cooled by the cooling water flowing through the water jacket.
In the case where the cylinder block is made of aluminum alloy, the triangular pillar is preferably formed with a bolt hole having a depth greater than the depth of the water jacket, and the water guide passage has an upstream end in communication with a pump chamber formed in the cylinder block that receives a water pump therein and a downstream end opening to the water jacket. Further, the water guide passage has a downstream end opening thin over the full depth of the water jacket and preferably has a cross section increasing in area from the upstream end to the downstream end. The water guide passage having an increasing cross sectional area causes cooling water to smoothly flow therethrough. In addition, the water guide passage having the thin downstream end that is thin and opens over the full depth of the water jacket avoids a significant increase in overall length of the cylinder block even though making the end opening as large as possible.
The cylinder block may have a water pump housing in which the pump chamber is formed as an external raise of a front portion of the one side wall of the cylinder block corresponding in position to the water jacket. The thermostat housing, that is formed as an external raise of the one side wall of the cylinder block, is located adjacently behind to the water pump housing. The arrangement in which the water pump is at the front portion of the side wall of the cylinder block makes it possible to drive the water pump by a crankshaft through, for example, a V-belt. Further, the arrangement in which the water pump housing is formed on the side wall of the cylinder block corresponding in position to the water jacket and located adjacently behind the thermostat housing makes the path length of cooling water from the thermostat to the water jacket through the pump chamber comparatively short. This provides an improved performance of introducing cooling water into the water jacket. On the other hand, the arrangement in which the water pump housing and the thermostat housing are formed on the side wall of the cylinder block near the water guide passage exert a constraint on the layout of the water guide passage in such the case that the water guide passage is arranged so as to be free of positional interference with these housings. Despite of the restraint, the engine block structure including the cylinder block described above guarantees the performance of introducing and distributing cooling water into the water jacket.